1. Field of the Invention
The present of the invention relates to a disc recording apparatus for an optical disc accommodated in a disc cartridge. More particularly, the present the invention relates to a supporting mechanism of an external magnetic field generating apparatus of a disc recording apparatus.
2. Background of the Invention
There has hitherto been proposed a disc recording apparatus for recording information signals using a recording disc, such as a so-called magnetic disc or a magneto-optical disc accommodated in a disc cartridge. The disc cartridge includes a cartridge main body and a shutter. The cartridge main body is formed of a pair of halves connected to each other. One of the halves has a central opening for a disc rotationally driving apparatus and an aperture for a recording and reproducing apparatus. The other of halve has an aperture for the recording and reproducing apparatus. The recording and reproducing apparatus includes an optical pickup unit and a magnetic head as an external magnetic field generating apparatus generating vertical magnetic field as external magnetic field. The shutter is slidable mounted on the cartridge main body and moves between an opening position of the apertures and a closing position of the apertures. The above mentioned magneto-optical disc as the recording disc includes a disc substrate made of transparent synthetic resin or glass, a recording layer made of a vertical magnetic recording medium and a protective layer or a lubricous layer formed on the recording layer. The recording layer is deposited on one of surfaces of the disc substrate. The information signals are recorded on the magneto-optical disc by radiating a focused light beam and applying vertical magnetic field at a predetermined position of the recording layer. The light beam is radiated from the one surface of the magneto-optical disc through the disc substrate, while the vertical magnetic field is applied from the other surface of the magneto-optical disc. The portion of the recording layer irradiated with the light beam is heated to a temperature higher than the Curie temperature so that its coercivity is lost. The heated portion of the recording layer is magnetized in the direction of the applied vertical magnetic field in the course of being cooled.
As a result, the information signals are recorded on the magneto-optical disc which is accommodated in the disc cartridge as changing the directions of magnetization of the recording layer by modulating the light intensity of light beam in accordance with the recording information signals or by modulating the direction of the vertical magnetic field in accordance with the recording information signals.
A disc recording apparatus for recording information signals using the above-described disc cartridge has a chassis, a cartridge holder, a rotationally driving unit, a magnetic head and an optical pickup unit. The cartridge holder detachably supports the disc cartridge and is provided on the chassis and moves between a loading position where the magneto-optical disc is set on the rotationally driving unit and an unloading position where the magneto-optical disc is detached from the rotationally driving unit. The rotationally driving unit rotationally drives the magneto-optical disc accommodated in the disc cartridge at a constant linear velocity or a constant angular velocity. The magnetic head generates the vertical magnetic field applying the magneto-optical disc. The optical pickup unit focuses and radiates the light beam on the magneto-optical disc. The magnetic head and the optical pickup unit are arranged facing each other with the magneto-optical disc in-between and connected to each other by an arm member. The magnetic head unit and the optical pickup unit are mounted for movement along with the arm member in a radial direction of the magneto-optical disc across its inner and outer peripheries.
The optical pickup unit has a light source, such as a laser diode, and optical elements for guiding and focusing a light beam radiated from the light source. The optical pickup unit is arranged at a distance from the recording layer substantially equal to the focal distance of an objective lens focusing the light beam on the recording layer so that the focusing point of the light beam is positioned on a boundary surface between the recording layer and the disc substrate.
On the other hand, the magnetic head includes a magnetic core and a coil wound on the core for generating the vertical magnetic field. When recording information signals on the recording layer, the magnetic head is supported substantially in sliding contact with the signal recording layer by the interposition of the protective layer or the lubricous layer of synthetic resin of the magneto-optical disc.
As a result, when unloading the magneto-optical disc from the above-described disc recording apparatus, the magnetic head needs to be separated sufficiently from the magneto-optical disc. The reason is that, if the magneto-optical disc is detached while the magnetic head is left in the position of being substantially contacted with the magneto-optical disc, the magnetic head tends to be slidingly contacted with the magneto-optical disc with an excessive pressure to cause damage or destruction of the magnetic head or the magneto-optical disc.
For this reason, the disc recording apparatus is so arranged and constructed that the cartridge main body is held by the cartridge holder and adapted to be contacted with and separated from the chassis of the rotationally driving unit, while the magnetic head is moved in a direction towards and away from the chassis by a distance larger than the cartridge holder. That is, in the present disc recording apparatus, the magnetic head is spaced apart from the cartridge holder when the cartridge holder is spaced apart from the chassis, is moved in a direction toward the unloading position, to permit the disc cartridge to be detached from the cartridge holder. In the above-described disc recording apparatus, when the cartridge holder is caused to approach to the chassis, the disc cartridge held by the cartridge holder is loaded on the chassis, is moved in a direction toward to the loading position, while the magnetic head is moved in a direction of approaching to the cartridge holder to approach to the magneto-optical disc.
The above-described movement of the magnetic head is performed by the cartridge holder movement as a driving source by a link mechanism which is moved in association with the movement of the cartridge holder.
Meanwhile, in the above-described disc recording apparatus, the link mechanism producing movement of the magnetic head is complex in structure and is made up of a large number of components, leading to complex designing, assembling and production.
Besides, since the link mechanism is complex in structure, malfunctions such as operating troubles occur frequently and therefore periodic maintenance and inspection cannot be dispensed with, while repair is rendered difficult. In addition, the disc recording apparatus cannot be reduced in size or weight because of the provision of the above-mentioned link mechanism.